Medical electrodes provide an electrical interface between a patient and monitoring equipment, e.g., an electrocardiograph device, or between a patient and stimulating equipment, e.g. defibrillation equipment.
Interest in reducing the transmission of communicable diseases in the hospital environment has increased the demand for the development of disposable medical equipment including electrodes. Referring to FIG. 1, a typical disposable electrode 10, meeting this demand, is packaged attached to a card 12 from which it may be removed for use.
A non-disposable lead wire 14 connects the electrode 10 to external monitoring or stimulating equipment (not shown). The lead wire 14 and the electrode 10 are joined at the interface of female connector 16, molded to one end of the lead wire 14, and male connector 18 attached to each electrode 10. The male connector 18 may be the boss of a low cost "snap" type connector, in keeping with the disposable nature of the electrode 10.
The contact resistance between the electrode 10 and the patient's skin may be reduced by the use of an electrolyte 19 between the skin-contacting surface of the electrode 10 and the patient's skin. An electrochemically active material 21 is also frequently incorporated into the skin-contacting surface of the electrode 10 to further enhance the electrically conducting characteristics of the electrode. This electrochemically active material may be a metal and its salt, such as silver and silver chloride.
The electrode 10 also may include adhesive 23 on its skin-contacting surface to physically anchor the electrode 10 against forces from the lead wire 14. The central positioning of the connector 18 within a ring of circumferential adhesive 23 provides this design with good resistance to peeling away with lateral force on the lead wire 14.
Although inexpensive, connectors 16 and 18 have a number of drawbacks. First, the connection force needed to separate connectors 16 and 18 is substantial and, therefore, connector 16 must be of sufficient size to enable medical professionals to grasp it firmly for removal. During connection of connectors 16 and 18, the downward engaging force applied to connector 16 may be uncomfortable to patients sensitive to compression; for example, those recovering from thoracic surgery. Further, often, it is desirable to leave the electrode 10 in place for a length of time to ensure the reproducibility of the measurements made. Male connector 18 projects a significant distance upward from the surface of the electrode 10 and can be uncomfortable when it is compressed by a mattress or other support against the patient. This problem is compounded when the female connector 16 is connected to male connector 18. For ambulatory patients, the projection of connectors 16 and 18 may interfere with ordinary clothing.
Connectors 16 and 18 include plated metallic material and, when x-rays are taken, produce an artifact in the x-ray image. This metallic portion is subject to undesirable corrosion when electrodes 10 are packaged in a "pre-gelled" state (with the electrolyte 19 applied) in hermetic packages.
It has also been determined that the snap system of connectors 16 and 18, modeled after a mechanical closure for clothing, does not provide a wiping action during connection and disconnection, and therefore is subject to developing detrimental high contact resistance.